1. Field of Invention
The present invention relates to catheter/needle placement and more particularly to a catheter assembly including a needle and a method for its use in delivering medicaments into the subarachnoid space.
2. Description of Related Information
Generally speaking, there are two basic techniques for introducing injectable medicament into the spinal area of a patient. The techniques both can be used to create spinal anesthesia: one being delivery of the medicament into the epidural space, "epidural," and the other, delivery into the subarachnoid space, "spinal" or "subarachnoid." The medicaments can be any type of liquid therapeutic material including antibiotics, steroids and the like, but generally are agents used for anesthesia and analgesia.
A survey of previous patent literature reports in this general area is found in U.S. Pat. No. 5,085,631 which teaches a method for placement of a subarachnoid catheter which utilizes a three component apparatus comprising an outer needle, an inner needle and a catheter intermediate the two needles.
A subarachnoid placement is recognized as providing a faster, more uniform distribution of an anesthetic agent, but several major side effects may result from improper subarachnoid placement.
Puncture of the dural membrane for entrance of a needle or catheter with a large gauge needle may result in postoperative leakage of cerebrospinal fluid from the puncture site, often resulting in severe headaches. When puncture of the dural membrane is made with a needle, a bolus introduction of the anesthetic agent generally is administered. The bolus results in rapid onset of anesthesia, but the anesthetic effect then generally lasts only a few hours. To overcome both the effects of a procedure requiring a large puncture of the dural membrane and the somewhat limited duration of subarachnoid bolus delivery, microcatheters were developed. The use of these microcatheters allowed intermittent installation of the medicament for maintenance of the anesthetic effect and minimized the size of the dural puncture, thereby reducing the incidence of post procedure headaches. Microcatheters also present severe side effects. Since they are small and flexible, microcatheters have limited flow capacity, the limited flow capacity may hinder mixing the medicament with cerebrospinal fluid. Microcatheters are additionally prone to kinking. Further, there have been occurrences of permanent nerve damage with microcatheters, apparently as a result of high local concentrations of the medicament developing during delivery at adjacent branching nerves. This potential for nerve damage resulted in restrictions on the use of certain microcatheter procedures.
Subarachnoid placement of medicaments, if done properly, is acknowledged to be desirable. Thus, a method and device that would minimize the size of the puncture of the dural membrane, allow accurate and controlled placement of a therapeutically effective amount of a medicament within the subarachnoid space, thereby avoiding nerve damage, coupled with an ability to rapidly initiate and maintain a therapeutic level for longer procedures would represent an advance to the medical arts. A method and apparatus that addresses these needs constitute the present invention.